The invention concerns a car body part of sheet metal of an aluminum alloy type AlMgSi, and a car body or component of a car body with at least one first component of sheet metal of the first aluminum alloy and at least one second component of sheet metal of a second aluminum alloy, where the first and second aluminum alloys are of type AlMgSi, and after artificial ageing of the body or body part, the second component in comparison with the first component has lower mechanical strength values.
For car body parts, car bodies or components of car bodies, artificial ageing takes place for example under the annealing conditions during paint baking or in a separately performed heat treatment.
The growing importance of the production of lighter cars with the purpose of energy saving has led to the development of a large number of aluminum alloys for car applications.
Different components in a car usually require different properties. For example, an aluminum alloy for outer panel applications must be easily deformable in order to allow stretch drawing, deep drawing and bending, and at the same time achieve a high strength after paint baking.
In Europe, for outer panel applications in particular for engine bonnets, already AlMgSi alloys are used, e.g. the alloy AA 6016, to a fairly great extent.
In particular, with regard to scrap metal reuse and recyclability, it would be particularly advantageous and suitable if for all aluminum panel applications in the body, aluminum alloys could be used which belong to the same family of alloys. U.S. Pat. No. 4,082,578 and EP-A-0 811 700 disclose aluminum alloys of type AlMgSi for inner and outer panel applications in car bodies.
Aluminum alloys in the structural area of a vehicle improve the driving behavior (vehicle rigidity, axle load distribution, center of gravity etc.). Such constructions can also have a high energy absorption capacity in the event of a crash. EP-A-1 165 848 discloses structural components made of sheet metal from an AlMgSi alloy.
In particular in Europe, the reduction of injury risk in car accidents has high priority. Due to improvements in car safety, this objective has been achieved very effectively. So far, however, very little has been done to reduce the severity of injuries to pedestrians and motorcyclists who hit the front of a car in an accident. Substantial improvements can be achieved by constructing the front parts of cars with corresponding energy absorption behavior.
Pedestrian protection measures on car bodies can be very effective in preventing serious and fatal injuries from collisions in the medium speed range. In most traffic accidents with pedestrians, a car collides frontally with the victim. The injury to the pedestrian is only partly caused by the initial impact. In many cases the pedestrian's torso bends and his head hits the bonnet.
Most head injuries are caused in adults by the upper end and in children by the front part, of the engine bonnet. The front edge of the bonnet is particularly critical in relation to injuries in the thigh or hip area. Detailed changes in the panel construction of the bonnet edge are necessary to reduce the rigidity and create sufficient crumple depth. This can be achieved by weakening or taking back the inner panel reinforcements on the bonnet, the bonnet closure and the closure cross braces.
By various active and passive measures, front panels and other large area body elements of cars have been made “softer”. Here, the components are designed or actively modified so that in an impact they can absorb a large part of the kinetic energy by plastic deformation. These measures lead to fewer serious injuries.
Passive measures include the design, construction and material. In relation to the material, various material compounds are known e.g. sandwich constructions with foam materials. So far, however, no tests have been undertaken on the use of relatively soft aluminum alloys.